1. Field of the Invention
The present invention relates to the separation of isoolefins from streams containing mixtures of an isoolefin and the corresponding normal olefin. The present invention is especially useful for the separation of isobutene from streams containing n-butenes.
2. Description of the Prior Art
Isoolefins of 4 carbon atoms are difficult to separate from the corresponding normal olefin by simple fractionation because of the closeness of their boiling points. In prior art processes as generally practiced commercially, the isoolefin is selectively absorbed by sulfuric acid and the resulting isoolefin-containing sulfuric acid extract is then diluted and heated or treated with steam to separate the isoolefin.
Isobutene and diisobutene are of significant value having diverse applications, for example, isobutene is one of the comonomers for butyl rubber and diisobutene is an intermediate in the preparation of detergents. The n-butenes are required in pure form for homopolymerization and as feeds for the oxidative production of butadiene. One manner of separating these components is to pass the mixture through what is called a cold acid extraction procedure wherein the stream is fed into a bath of concentrated sulfuric acid. Separation is achieved by virtue of the solubility of the isobutene in the sulfuric acid, the n-butenes and other hydrocarbons present passing overhead.
In an improved process reported in U.S. Pat. No. 3,531,539 to Tidwell, the C.sub.4 feed stream containing isobutene was contacted with a molecular sieve at an elevated temperature and under sufficient pressure to maintain a liquid phase, wherein the isobutene is converted to diisobutene which is easily separated from the stream by conventional separation techniques.